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Like the start of a horror movie, ancient creatures emerge from the cold storehouse of melting permafrost: from amazingly preserved extinct megafauna like the woolly rhino, to the 40,000-year-old remains of a wolf giant and bacteria over 750,000 years old.
Not all are dead. Centuries-old foams were able to come back to life in the heat of the laboratory. There were also, incredibly, tiny 42,000-year-old roundworms.
These fascinating glimpses of organisms from Earth’s distant past reveal the history of ancient ecosystems, including details of the environments in which they existed. But the melting has also raised concerns that old viruses will return to haunt us.
“The melting will not only result in the loss of these old archived microbes and viruses, but will also release them into the environment in the future,” write the researchers in a new study, led by first author and microbiologist Zhi-Ping Zhong of the state of Ohio. University.
Using new metagenomic techniques and new methods of sterilizing their ice core samples, researchers are working to better understand what exactly is lurking in the cold.
In the new research, the team was able to identify an archive of dozens of unique 15,000-year-old viruses from the Guliya ice sheet of the Tibetan Plateau and better understand their functions.
“These glaciers formed gradually, and along with the dust and gases, a great many viruses were also deposited in this ice,” Zhong said. These microbes potentially represent those in the atmosphere at the time of their deposition, the team explains in their article.
Previous studies have shown that microbial communities correlate with changes in dust and ion concentrations in the atmosphere, and may also indicate climatic and environmental conditions at the time.
In these frozen records from ancient times, 6.7 kilometers (22,000 feet) above sea level in China, the researchers found that 28 of the 33 viruses they identified had never been seen before. .
“These are viruses that would have thrived in extreme environments,” said Ohio State University microbiologist Matthew Sullivan with “gene signatures that help them infect cells in cold environments – just genetic signatures surrealists to how a virus is able to survive in extreme conditions. ”
By comparing their genetic sequences to a database of known viruses, the team found that the most abundant viruses in the two ice core samples were bacteriophages that infect Methylobacterium – bacteria important for the methane cycle in ice.
They were mainly linked to viruses found in Methylobacterium strains in plant and soil habitats – in line with a previous report that the main source of dust deposited on the Guliya ice cap is likely from soils.
“These frozen viruses probably originate from the soil or plants and facilitate the acquisition of nutrients for their hosts,” the team concluded.
While the specter of ancient viruses looks particularly ominous in the midst of a pandemic, the greatest danger is that melting ice will release other – massive stores of sequestered methane and carbon. But it is clear that the ice could also contain information about past environmental changes, as well as the evolution of viruses.
“We know very little about viruses and microbes in these extreme environments, and what really is there,” says Earth scientist Lonnie Thompson, who notes that we still have many important unanswered questions. .
“How do bacteria and viruses react to climate change? What happens when we go from an ice age to a warm period like the one we are experiencing now? “
There is still a lot to explore.
This study was published in Microbiome.
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